Solids level control



1952 J. D. LANKFORD ETAL 2,620,933

soups LEVEL CONTROL Filed Jan. 8, 1951 2 SI-EETS SHEET 1 Fig.

INVENTORS Jonathan D. Lonkford Fred J. Troher Fred W. Taylor ATTORNEY I 9, 1952 J. D. LANKFORD ET AL 2,520,933

SOLIDS LEVEL CONTROL Filed Jan. 8, 1.951 2 SHEETS-SHEET 2 F fg. 2

INVENTORS Jonathan D. Lonkford Fred J. Trotter Fred W. Taylor BY ATTORNEY Patented Dec. 9, 1952 SOLIDS LEVEL CONTROL Jonathan D. Lankford, Fred J. Trotter, and Fred W. Taylor, Rifle, 0010., assignors to the United States of America, as represented by the Secretary of the Interior Application January 8, 1951, Serial N 0. 204,921

13 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor.

This invention is concerned with a device and a method for maintaining a predetermined level of particulate solid material within a container.

In the handling of particulate solid material, for example, in the storing or processing of such material, it is often necessary or desirable to maintain a constant level of solids within a container from which the solids are continuously or intermittently withdrawn. Maintaining the necessary control over the solids level is often a difficult problem particularly where the solids being handled are made up of coarse and irregularly sized particles which have poor properties of flow. Likewise, in the processing of particulate solids, the processing conditions often aggravate the problem of control. The problems encountered in the retorting of oil shale to produce liquid hydrocarbons is an illustration of a particularly diilicult situation involving the necessity for controlling the solids level. To insure efficient conditions for retorting, it is usually necessary to maintain the level of crushed oil shale in the retort within rather close limits. Since the particles of crushed shale are coarse and irregular in size (ranging from about A; to 2 inches) and since the temperature in the retort is quite high (for example, from 800 to 1200 F.) the problem of controlling the crushed shale level within the retort is quite difficult.

Prior methods and devices for controlling or indicating the level of particulate solids within a container suffer from a number of disadvantages, which in many instances makes them entirely unsuitable. Indicating or control devices such as diaphragms, for example, which operate in response to the pressure exerted by the solids on the walls of the container are not rugged enough to withstand severe operating conditions such as extremely high temperatures. Float devices are often undependable particularly when coarse and irregularly-sized particles are being handled since these tend to become buried in the mass of the solids instead of floating on the surface thereof. Similarly, the lack of flexibility and adaptability to various types of solids often make these and other prior devices undesirable for many uses.

An object of the invention is to provide a device and a method for maintaining a predetermined level of particulate solid material in a container which operates efficiently under the most severe operating conditions.

It is a further object of the invention to provide a device and a method for controlling the level of particulate solids which is dependable in operation regardless of the type of solids being handled.

Another object of the invention is to provide a device and a method for controlling the level of solids in a container which may be operated to control the solids level within wide or narrow limits as desired and which can be adapted to solids of any density or particle size distribution.

Additional objects of the invention will become apparent from a consideration of the subsequent description together with the accompanying drawings.

The present invention for accomplishing the foregoing objects involves the use of a piston located at a point adjacent the solids level which is to be maintained. Over comparatively short time intervals, the piston is periodically urged forward into the container space and then withdrawn therefrom. As the piston moves back and forth, in and out of the container space, it feels, so to speak, for the solids level in the container. As long as the solids level is below the piston, it continues to operate back and forth within a fixed period of time. The forward thrust of the piston is so adjusted that when the solids level rises above the level of the piston, entry of the piston into the container space is hindered and the periodic reciprocation of the piston is thereby stopped. Timing means are provided to detect the failure of the piston to continue its reciprocation. After a lapse of a predetermined time intervallonger than the time required for the piston to complete at least one reciprocation, the timing means may give a signal indicating that the solids level has risen above the piston, or may automatically control the operation of means for adjusting the solids level, for example, by discontinuing the feed of additional solids into the container, or by starting the discharge of solids therefrom.

For better understanding of the invention, reference is now made to the accompanying drawings in which Fig. l is a semidiagrammatic view showing one particular embodiment of the invention in operative relationship with a container adapted for use in processing particulate solid materials such as crushed oil shale; and

Fig. 2 is a view partly in section showing in detail some of the more important elements, of the device illustrated in Fig. l; and

the material to be processed is introduced at the top of the container by the feede 3fand'the finished processed material withdrawn from the bottom of the container by means'not, shown. Gaseous products evolved during'theprocessing;

for example, hydrocarbon vapors in the case of retorting of oil shale, are withdrawn at the top of the container through conduit 4. Assuming that it is desired to maintain the solids incontainer I at a predetermined level designated'b'y the dotted line L, a reciprocatihlg' piston"5: (see- Fig. 2) is provided at a point adjacent the predetermined-level L. Housing 6 surrounding the piston and its operating. mechanism is attached to the outer wall of the container 1}""GQIXIP1GSSGC1 air, supplied by line 1, is conducted throughvalve 8 andline 10 to the mechanism for operating the piston 5.1 'As' will appear in more detail .from the subsequent description, valve 8 is. a solenoid operated valve which is controlled by the timing device'S, for" periodically admitting compressed airinto and-releasing compressed." air from, the mechanism which operates-thepiston.

An electronic timi'n'g device. H: is connected, by means of cable 12,110 a switch controlled by piston 5 in a manner tobbe subsequently described. Throughthe appropriatesetting of the time delay variables of-the electronic timing device II, the periodic reciprocations is detected whereupon the timing device ll automatically breaks'the circuit supplying power byway ofleadsjl l'and led. to the motor l3 which operat'es the feeder 3, therebycutting offthe" feed ofsolid material to the container. 1

*Referring now to Fig. 2, it will be seen that the piston 5 slides in a housing [5 fastened to an outside. wall 'of'the container by the bolts It. The 'piston 5, togetherwith the piston housing l5, are disposed opposite an opening IT. in a Wall bf the container s'othatjas the piston moves. forward and backward it enters, and is withdrawn from, the. container: space. In the embodiment shown, 'thepiston is driven by means of compressed air. The compressed air is' supplied by way. of line 1. to the 3-way solenoid operated valve 8; The timing device 9 (see Fig. 1) isprovided'to'periodicallyenergize anddeenergize the solenoid coil [8. The device 9, for accomplishing this may be of any'suitable construction and is preferably provided with controls l9 .for varyingthe time intervals between the periodic energization and'de-energization of the solenoid coil 18';

As shown in" Fig. 2, thefs'olenoid [8 has been de-energized, causing theupper portion. 20 of the valve 8 to open for the admission of compressed air, and causing the lower or vent portion 2170f the valve 3 toclose. The compressed airflows by way-"of line l;0to the, diaphragm chamber 22:exerting aforce against the diaphragm 23. Movement or-the diaphragm'23 is communicatedto-thediaphragm button 24 and to the boss 25'to which the diaphragm button is attached.

Piston rodZE, rigidlyattached at one end to boss 25, and at the opposite end to; the piston 5, is slidably mounted in abushing. 2 'l;carried failure of'the pistonto executeits.

4 by piston housing [5 and in a second bushin 28, having'a flange 29. Flange 29 is threaded at its periphery and screws into the open end of diaphragm housing 30,. internally threaded as'at 3l. i

To return the piston to its original position after the pressure is released from the chamber 22, a coil spring 32 is provided held in compression between flange 29 and a shoulder 33 on boss 25. The tension on the spring 32 may be adjusted by screwing the flanged bushing 28 inwardly or outwardly alon the axis of the diaphragm housing '30.

Above the piston rod 26, a mercury switch 34 is mounted rigidly on a swinging arm 35. The opposite end of arm 35 is pivotally connected at 36 to an upright post 31 rigidly connected at 38' to the piston rod 26 for movement therewith. The arm 35 likewise slides in a slot 39 provided in a bar 40 rotatably mounted on supports 41 (see Fig.3). By virtue oi this. system of linkages, the arm 35; carrying the mercury switchylid cha eesfits, posit on. as the piston.

travels back and for h, assuming the position shown in dotted lines, when. the piston isin a the 'grid. 50 of a sharp cut-off amplifier tube 5|. The tube 51 is provided; with a filament '52 heated from a source 53;. The cathode. 54 is grounded as at. 55;. The 'plate 55. isv connected by lead 57 to. the coil 58; of relay 59;. The opposite end. of the 'relay. coil 58 is connected to the positive terminal of the battery 60,.grounded at El, which furnishes. the plate. voltage.

The relay 59,-.controlsi the circuit. supplying power tothe. motor 13 'for driving the feeding me'chanism13. Leads. 14. and .l4-a of'this cir-. cuit are connected'to'. theopposite terminalsof relay 59, line voltage being suppliedto the cir-' cuit throughl'ea'ds 6.2.: With nocurrent flowing in the coil 53. the relay 59: is normally closed, thus completing the circuit. supplying the power to the motor l3. When current flows in coil 58, the relay'is held in the open position, breaking'the circuit, and thus stopping the operation of the motor l3.

The right hand terminal 441) of the electronic timer H. is grounded at: 63, while the left hand terminal 42b is connected to the negative. terminal of thebattery fi lwhich is. grounded at 65.

The operation of thegembodiment. shown in the drawings willnow. be described. Assuming that the level, of solids in the'container. .I. has, fallenbelow thelevelwhich it isdesired to main. 'tain, the piston 5.Wil1, beable toenter the container space without hinderance. The feeder 3 will be in operation, feeding; additional solids. 7 into the container to restore the solids level to.

the predetermined level L.

r o i i r cati nso the p s n. 5 ar timed; by the device awhich; controls solenoid per ted. valv ,8. f r r odi a ly admit in 0 1.

respectively, of; the

pressed air into, and releasing compressed air from, the diaphragm chamber. 22. As previously explained, the device 9 controls the operation of the valve 8 by periodically energizing and de-energizing the solenoid coil I8. When the solenoid coil I8 is in the de-energized state, the upper portion 2|] of the valve is open to admit compressed air to the diaphragm chamber 22, while the lower portion 2| is closed. Conversely, when coil I8 is energized, the upper portion of the valve 20 is closed, while the lower portion 2| is open, allowing the compressed air in the chamber 22 to vent to the atmosphere.

The period of time between energization and de-energization of coil I8, and likewise the period of time between de-energization and energize.- tion of the coil may be set in advance by proper adjustment of the controls I9 on the timing device 9. Thus, for example, the period between energization and de-energization of the coil may be set at 45 seconds, while the period between de-energization and energization of the coil may be set at 10 seconds. With these settings, the piston will make a complete reciprocation every 55 seconds.

The forward thrust of the piston is controlled so that when the level of solids rises above a predetermined point on the piston, the forward thrust of the piston will be no longer sufficient to overcome resistance offered by the pressure of solids against it. For example, as illustrated in Fig. 2, the forward thrust of the piston 5 may be adjusted so that when the solids reach the level L at the center of the piston, the piston will no longer be able to move into the container space. The solid and dotted lines R and R2, respectively, indicate the angle of repose of solids in the container when the level of solids is below and at, respectively, the predetermined level L.

In the embodiment shown, the forward thrust exerted by the piston 5 depends upon a number of factors and can be varied at will by the adjustment of one or more of these factors. Thus, the forward thrust exerted by the piston is directly proportional to the area of diaphragm 23, while it is inversely proportional to the diameter of the piston, and also inversely proportional to the backward thrust exerted by coil spring 32. The proper adjustment of these variables will depend upon the material being handled and whether or not the level of solids is to be controlled between wide or narrow limits.

As long as the level of solids within the container I is below the predetermined level L the piston 5 will continue to move back and forth within a fixed period determined by the setting of the cycle timing device 9. As shown in solid lines in Fig. 2, the piston 5 has moved to its most forward position causing the mercury switch 34 to assume the position likewise shown in solid lines. In this position, the mercury pool 34a bridges the gap between terminals 42 and 43L leaving open the gap between terminals 44 and 43R, thus closing the circuit between terminals 422) and 43b of the electronic timer II. Closing of this circuit charges the variable condenser 41 and at the same time applies a negative voltage on grid 59 of tube 5|. The negative bias on the grid 59 renders the tube 5| nonconducting, consequently no current flows through the relay coil 58, the relay therefore remaining in its normally closed position, the motor I3 operating feeder 3 continuing to operate.

When the piston 5 is withdrawn from the container space, assuming the position shown in dotted lines, the mercury switch 34 moves to a position likewise shown in dotted lines. In this position, the mercury pool 34a flows to the opposite end of the switch 34, opening the gap between terminals 42 and 43L and bridging the gap between. terminals 43R. and 44, thereby completing the circuit across terminals 43b and 44b of the electronic timer I I while at the same time breaking the circuit across terminals 422) and 435. Making of the circuit across terminals 431) and 44b throws the condenser 41 and the grid 59 to ground thereby causing the condenser 41 to begin to discharge through resistance 46 at a rate dependent upon the capacitance of the condenser 41 and the value of the resistance 45. After a certain period of delay, the potential of the condenser 41 drop to a value such that the tube 5| becomes conducting, allowing current to flow through the coil 58 thereby breaking the circuit supplying power to the motor I3. Conveniently, the electronic timer I I is provided with a set of controls, calibrated in intervals of time, for example, seconds, for setting the desired time delay factor between grounding of the condenser 41, when the piston executed its backward stroke, and the energization of relay 59. Thus, a dial 46a, may be provided (see Fig. 1) for controlling the value of the resistance 46; while a dial 41a may be provided for controlling the capacitance of condenser 41.

The time delay factor of the electronic timer II, that is, the interval between the time the grid 59 and condenser 41 are grounded by completing the circuit across terminals 43b and 44b, and the time the tube 5| becomes conductive, is set at a value greater than the time required for the piston to complete one reciprocation. Thus, for example, if it takes the piston seconds to complete one reciprocation, the delay of the electronic timer will be set at a value greater than 55 seconds, for example, seconds. In this way, so long as the piston 5 continues to execute its periodic reciprocations, the tube 5| will remain nonconducting, and the feed mechanism 3 will continue to operate since the condenser 41 will be recharged each time the piston 5 executed its forward stroke, thus preventing the potential on the condenser 41 from dropping to a level at which the tube 5| becomes conducting.

When the solids leve1 rises above the predetermined level L the piston will not be able to execute its for-ward stroke and the mercury switch 34 will remain in the position shown in the dotted lines, and the circuit across terminals 43b and 44b of the electronic timer will remain completed. After the elapse of the delay interval at which the electronic timer is set, for example, 65 seconds, the tube 5| becomes conducting, opening the relay 59 and cutting off the motor I3. So long as the piston is unable to penetrate into the container space, current will continue to flow in coil 58 of the relay 59, thereby cutting off the feed of additional solids into the container. When the level of solids drops once more below the predetermined level L, the piston will once again begin to execute its periodic reciprocations thereby charging the condenser 41 at frequent enough intervals to prevent the tube 5| from conducting current and thus permitting additional solids to be fed into the container.

The device provided by the present invention is capable of wide application in the handling of particulate solids of all descriptions. Since sub- 7." stantially all the working. parts may. be. locatedon an outsidewallof thev container, these arenot efiected by severe conditions, such lasahighitem-r perature or. a corrosive atmosphera which ,may exist: withinthe container. itself. A: relatively small piston passing. through an .openinginthe. wall ofthe containera relatively.shortdistance into the. container. is;- the: only 'working'partiexr osed to: the condition insidejthecgntainer. By: the use of a suitable piston housineiand suitable. packing for .the. bushingin.,whichtheepiston rod slides, a gas-tight seal ;can;be;established between the. interior ofthe. container andi heu peratine mechanism immediatelyadiaeent; the. pi t n; housing.- Likewise, since the, piston; penetrates, only a short distanceinto the c n ainer; there. is little; likelihoodof i its; becoming j ammed by. the, solidsin the. container...

Besides providin an. instrument. of ntrol which is ru ged and-;.depe b e in op t on. the Dresent'invention likewise-provides; a: methodand device which. is extremelyfiexible so that with minoradiustments, it' c'.a n- ;loe quickly adapted for, use with parti u atesol ds-having wid yva i e characteristics; hus,, or,exa p m be used-tin: the, handling, ormaterials such asygraln and pulverant materials such as cement Tor pulverizedcoal as; well, as; with coarse, I irregularly shapedparticles such a crushed rock; Aswas previously explained,- the thrust exerted by the piston can be adjusted'easily; in a number of ways to; suit'the device; for materials ofieringgreater or. less resistanceto th movement-of the piston. likewise, by a few simple adjustments, thesolids level; may be controlled; within .wideor narrow limits, For example, by adjusting; the delay intervalpf the-electronic timer-in respect to the periodic reciprocations of thepiston,. an extremely-sharp control. over the .solidslevelmay bemaintained, or; if desired,,the= level may be controlled -Withln maximum andminimum permissibledimits. It :isoften advantageous ..n ot to control the level too .closely since this 7 occasions frequent starting and stopping of. the motors. operating the feed mechanism,- causing excessive wear.

It is to be understood thatthespecific. embodimentof the invention described aboveis intended merely to be illustrative and that. the invention is capable of many modifications Withoxitdepartingfrom the spirit thereof. For example, it.is clear that anysuita-bletype of mechanism'maybe employed for. operatingthe piston in additionto thecompressed air system described, The piston, for, example,v maybe. operated ,by a c,am,,,p eriojdically urgingthe pistoninaforward direction. When usinga cam tojdrivethejpiston directly, the cam is preferably, spring, loaded so that the amount of thrustiexertedbiy the piston in itsforward movement can be controlled;

Similarly, instead of the electronic. timing device described, any oth er timing means for detecting the failure. of "the piston to execute its timed reciprocations, may beyemployed; Thus, for-example, other typesof electronic timing circuits than that, described may be'employed-pr if desired a mechanical timing device, operated through suitable arrangement of gear trains-may be used.

Although ;it-is-most convenient that thetim-ing device be-adapted to automatically control the feeding or discharging mechanism; this is not necessary. Instead, the timing-device may-be utilized to operate a set of signalsindicating when the solidslevel-risesabove or-falls below the predetermined level'to be maintained.

8;. operator, observing these. signals, couldthen controlthe mechanism vreeding;solids-o or dis harg ing. solids from the container.

.Itsis likewise apparent that twoor more of the devices constructed, in accordancewith the invention may be employedinconjunction with tobe limited thereto, nor in anyavayexcept' by.

the scopeof the appended claims.

We claim: l. A device for maintaining a, predetermined level of particulatesolid material ,in acontainer comprising a piston located on a sidewall of said container adjacent said predetermined level, continuously operated driving means for urging said piston laterally into said container'at regular predetermined time intervals, means for withdrawing said piston after each for-ward; stroke thereof, the lateral forward thrust ofsaidpiston being adjusted so as to be insufficient to overcome the resistance-ofiered-by said-solid material when the solids level in said container-rises above said predetermined level, whereby said piston is able to execute complete reciprocations at said regular predetermined intervals only when the. level of sol-ids infsaidcontainer remains below said predetermined level, and means including a timer for detecting the time required by said piston to execute .a completereciprocationso as to detect the failure of said piston toexecute complete reciprocations at said regularpredetermined time intervals,

2. A device for maintaining-a predetermined level of particulate solid material ina container.

comprising a piston located on a sidewall of said container adj acent said predetermined level, continuously operated driving means-,forurging said piston laterally into said container atregular predetermined time intervals, means for withdrawing-said piston after each forward stroke thereof, the lateral forward thrust of said :piston beingadjusted so as to be insufiicient to overcome the resistance offered by said solid material when the solids level in said .containerrises :abovesaid predetermined level, whereby said piston is able to execute complete reciprocation at said regular predetermined intervals only when the level of solids in said container remains .belowsaid predetermined level, and means including a timer for detecting the time required ,by saidppiston to execute a complete reciprocationso as to detect the failure of .saidpistontoxcontinue toexecute complete reciprocations at-said regularvprede-r termined intervals, and means controlled by-said timer for adjusting the solidslevel in .said .con tainer.

3. A device for maintain-inga predetermined level of particulate-solid material ina container comprising .a piston located atan opening in a wall of said container adjacent said predetermined level, continuously operateddriving means or; r ng a d' pisto ateral y; o ai open n o' d;.1 on ainer;atz eula d rmined, time intervals; means; for at; leastpar,- tially withdrawing. said; piston; from said; container, after. each forward strokerthereof; thalateral forward thrust of .s'aid .pistonbeingqadjusted so as to be insufficient to overcome the resistance offered by said solid material when the solids level in said container rises above said predetermined level, whereby said piston is able to execute complete reciprocations at said regular predetermined intervals only when the level of solids in said container remains below said predetermined level, and means including a timer for detecting the time required by said piston to execute a complete reciprocation so as to detect the failure of said piston to execute complete reciprocations at said regular predetermined time intervals.

4. A device for maintaining a predetermined level of particulate solid material in a container comprising a piston located on a sidewall of said container adjacent said predetermined level, continuously operated driving means for urging said piston laterally into said container at regular predetermined time intervals, means for withdrawing said piston'after each forward stroke thereof, the lateral forward thrust of said piston being adjusted so as to be insufficient to over come the resistance offered by said solid material when the solids level in said container rises above said predetermined level, whereby said piston is able to execute complete reciprocation at said regular predetermined intervals only when the level of solids in said container remains below said predetermined level, and means including move forwardly into said container after the lapse of a predetermined time interval longer than the time required for said piston to execute a complete reciprocation in an empty vessel.

5. A device for maintaining a predetermined level of particulate solid material in a container comprising a piston located on a sidewall of said container adjacent said predetermined level, continuously operated driving means for urging said piston laterally into said container at regular predetermined time intervals, means for withdrawing said piston after each forward stroke thereof, the lateral forward thrust of said piston being adjusted so as to be insufiicient to overcome the resistance offered by said solid material when the solids level in said container rises above said predetermined level, whereby said piston is able to execute complete reciprocations at said regular predetermined intervals only when the level of solids in said container remains below said predetermined level, a switch actuated by the movement of said piston, an electrically operated timer controlled by said switch, said timer being adapted to detect the time required by said piston to execute a complete reciprocation so as to detect the failure of said piston to execute complete reciprocations at said regular predetermined time intervals, means controlled by said timer for adjusting the solids level in said container, said timer being adapted to effect a change in the operation of said solids level adjusting means when said piston fails to move forwardly into said container after the lapse of a predetermined time interval longer than the time required for said piston to execute a complete reciprocation in an empty vessel.

6. A device for maintaining a predetermined level of particulate solid material in a container comprising a piston located on a sidewall of said container adjacent said predetermined level, continuously operated driving means for urging said piston laterally into said container at regular predetermined time intervals, means for withdrawing said piston after each forward stroke thereof, the lateral forward thrust of said piston being adjusted so as to be insufficient to overcome the resistance offered by said solid material when the solids level in said container rises above said predetermined level, whereby said piston is able to execute complete reciprocations at said regular predetermined intervals only when the level of solids in said container remains below said predetermined level, a switch actuated by the movement of said piston and adapted to open and close an electric circuit on each complete reciprocation of said piston, a timer associated with said electric circuit and adapted to detect the time required by said circuit to open close so as to detect the failure of said circuit to open and close, in accordance with the movement of said piston, at said regular, predetermined time intervals, and means controlled by said timer for adjusting the solids level in saic container.

'7. A device for maintaining a predetermined level of particulate solid material in a container comprising a housing fastened to an outside wall of said container opposite an opening in said wall adjacent said predetermined level, a piston in said housing, continuously operated driving means for urging said piston laterally through said opening a relatively short distance into said container at regular predetermined time intervals, means for at least partially withdrawing said piston from said container after each forward stroke thereof, the lateral forward thrust of said piston being adjusted so as to be insufficient to ovecome the resistance offered by said solid material when the solids level in said container rises above said predetermined level, whereby said piston is able to execute complete reciprocations at said regular predetermined intervals only when the level of solids in said container remains below said predetermined level, and means including a timer for detecting the time required by said piston to execute a cornplete reciprocation so as to detect the failure of said piston to execute complete reciprocations at said regular predetermined time intervals.

8. A device for maintaining a predetermined level of particulate solid material in a container comprising a housing fastened to an outside wall of said container opposite an opening in said wall adjacent said predetermined level, a piston in said housing, continuously operating, gas actuated driving means for urging said piston into said container at regular, predetermined time in" tervals, the lateral forward thrust of said piston being adjusted so as to be insuflicient to over come the resistance offered by said solid material when the solids level in said container rises above said predetermined level, whereby said piston is able to execute complete reciprocations at said regular, predetermined intervals only when the level of solids in said container re mains below said predetermined level, a switch actuated by the movement of said piston, an electrically operated timer controlled by said switch, said timer being adapted to detect the time required by said piston to execute a complete reciprocation so as to detect the failure of said piston to execute complete reciprocations at said regular predetermined time intervals, means con vtrolled by said timer for adj,ust-ingt-he solids level in said container, said'timer being adapted to efiect a changein theoperationof-said'solids level adjusting means whenv saidipiston "fails to move forwardly into said container after the stroke by gas under pressure.

l0. A device in accordancewit-h "claim 2 in which said piston is driven during its .forward stroke' by gas under pressure. H I

11. A device in accordance with claim 4 in which said piston is driven during its forward stroke by gas under pressure V,

12. A device Vforrmaintaining a predetermined levelof particulate solid material in a'container comprising a piston located on a sidewall or" said container adjacent said predetermined level, continuously operated driving means for urging said piston laterally into'saidcontainer atregular predetermined time intervals, means for withdrawing said piston after each forward stroke thereof, the lateral forward thrust of said piston being adjusted so as to be insufiicient to overcome the resistance offered by said solid material when the solids level in :said container rises above said predetermined level, whereby said piston is ableto execute complete reciprocations at said regular predetermined intervals only when the level of solids i -said container remains ,below said predetermined level.

13. A-device for maintaining a predetermined level of particulatesolidinaterial in a container comprising a piston located lama-sidewall of said container adjacent-saidpredetermined level, continuously operated driving-meansfor urging-said piston laterally into-saidcontainer at regular predetermined time intervals, means for withdrawing said piston 'aftereach Y forward stroke thereof, the lateral forward thrust of said piston being adjusted so as to beins'uiiicient'to overcome the resistance offered b'y said solid material when thesolids levelin'said ccntainer rises above said predetermined level, whereby said piston is able to execute ccmpletereciprocations at said regular predetermined intervals 'only-whenthe level of solids in said container remains below said predetermined level, and a switch actuated by the movement of saidpis'ton adapted -to open and close an electric-circuit on each cemplete reciprocation of 'said piston.

JONATHAN D. LANKFORD.

FRED -J. TROTTER.

FRED W. TAYLOR.

REFERENCES CITED .The following references "are ofrecord'inthe file of this patent: V

UNITED "STATES PATENTS Number Name 'Date 2,299,727 Blauveltet al Oct.'27, 1942 2,565,136 Kretzme'rjJr "Aug. '21, 1951 

